1. Field of the Invention
This invention relates to an apparatus for reducing noise generated by a supersonic jet.
2. Description of Related Art
For a supersonic jet airplane, the thrust force is generated by the reaction of the exhausting of supersonic jet issuing from supersonic jet engines. When a silencer is not provided to the jet engine installed on the supersonic jet airplane, there is fear that very high level noise, which is called screech tone, is generated outside a nozzle of the jet engine by a supersonic jet exhausted from the nozzle. The screech tone causes high level noise in an airport and its surrounding, and when a structure of the airplane is exposed to the strong screech tone for a long time, there is fear that metallic aircraft structure can be destroyed. As is known in the art, the screech tone is generated by a self-sustained oscillation of jets caused by a feedback loop consisting of downstream-convecting large scale coherent eddies around the supersonic jet and upstream-propagating acoustic waves in the ambient.
Recently, several investigations in reduction of supersonic jet noise have been carried out. As a result, it is known that providing small projection within nozzle exit of a jet engine is effective to reduce the screech tone. However, this apparatus for supersonic jet engine reduces the screech tone by merely regulating or fairing a supersonic jet flow utilizing the small projection at the exit of the supersonic jet nozzle, and therefore sufficiently noise reduction could not be obtained. Thus, inventors have studied to develop a new type apparatus for reducing the screech tone on the basis of the entirely different principle from the prior art.